Chapter 2 Lecture Chapter 2: Motion Along a Straight Line © 2016 Pearson Education, Inc.

Goals for Chapter 2 Become comfortable with displacement, velocity, and acceleration in one dimension. Explore motions at constant acceleration. Be able to graph and interpret graphs as they describe motion. Be able to reason proportionally. Examine the special case of freely falling bodies. Consider relative motion. © 2016 Pearson Education, Inc.

Motion Motion is divided into two areas of study: Kinematics This will be our focus in Chapter 2 (1-dimension). [2-D in Chapter 3] Kinematics describes the movement of the object. Dynamics Will come in Chapter 4 and after Dynamics answers the "Why is this object moving?" question. © 2016 Pearson Education, Inc.

2.2 Displacement and Average Velocity: "Are we there yet?" Displacement, the distance from *here* to *there*  a vector quantity (but only a ± in 1-dimension) Units SI: Meters (m), CGS: Centimeters (cm), US Cust: Feet (ft) Average velocity  a vector quantity Stop, speed up, slow down Focus on total time and total displacement © 2016 Pearson Education, Inc.

Average Velocity - Figure 2.1 © 2016 Pearson Education, Inc.

Average Velocity - Figure 2.2 Total (both trips) displacement (vector) = 0 m Total (both trips) distance (scalar) = 258 m × 2 = 516 m © 2016 Pearson Education, Inc.

Motion of the Dragster - Figure 2.6 The average velocity between two positions is the slope of a line connecting the two corresponding points on a graph of position as a function of time. © 2016 Pearson Education, Inc.

2.2 Instantaneous Velocity: "What did the radar gun say?" … Look on a digital dashboard and compass Instantaneous velocity is found with a tangent line to a position vs time graph. We need to be sure of sign conventions.  a vector quantity (but only a ± in 1-dimension) What direction is the motion undergoing? Direction draws a distinction between scalars and vectors. © 2016 Pearson Education, Inc.

Motion of the Dragster - Figure 2.7 © 2016 Pearson Education, Inc.

Interpretation of Motion via Graphing - Figure 2.8 © 2016 Pearson Education, Inc.

2.3 Average and Instantaneous Acceleration: "How is a 'dragster' different from my car?" When velocity changes in time  acceleration Instantaneous acceleration (vector): The idea develops as it did with position vs time for velocity: now we plot velocity vs time. It is found as the tangent line to v vs t graph. We need to consider sign conventions and "braking" as a new idea and application of vectors. © 2016 Pearson Education, Inc.

Motion in Pictures and Graph - Figure 2.12 © 2016 Pearson Education, Inc.

Acceleration from a Velocity vs Time Plot - Figure 2.15 Average acceleration  slope between two points Instantaneous acceleration  line tangent at point © 2016 Pearson Education, Inc.

2.4: Describing Motion at Constant Acceleration "Can I stop before I hit the tree?" When will the police motorcycle overtake the speeding car? Relationship velocity-time displacement-time velocity-displacement Equation © 2016 Pearson Education, Inc.

Total Displacement? - Figure 2.21 © 2016 Pearson Education, Inc.

Different Plots Featuring Acceleration - Figure 2.20 © 2016 Pearson Education, Inc.

2.5: Proportional Reasoning Thinking about your numbers For example: there are linear, quadratic, inverse, inverse-square proportions between two variables x and y. © 2016 Pearson Education, Inc.

"Thank You Galileo" - Free Fall and Figure 2.24 As the story has it, he dropped objects from the Leaning Tower of Pisa; one heavy, one light. They hit simultaneously, disproving Aristotle's assertion that heavier objects fall faster. A feather and a hammer falling on the moon during the Apollo 15 mission by astronaut Dave Scott. The key is that Galileo is right for motion in the absence of air resistance. © 2016 Pearson Education, Inc.

Free Fall in a Vacuum - Figure 2.24 The apple and the feather are in a vacuum chamber and the photograph is taken with a strobe light. © 2016 Pearson Education, Inc.

"Against the Wind" – Figure 2.29 Good examples include: a plane and a head/tail wind a boat on a river a cruel joke at a stop light © 2016 Pearson Education, Inc.